Apparatus for coating web material



M. CAMPBELL APPARATUS FOR COATING WEB MATERIAL Aug. 4, 1964 2 Sheets-Sheet 1 Filed July 26, 1960 KIS FIG.3

FIG. 2

INVENTOR. MARK CAMPBELL Aug. 4, 1964 CAMPBELL 3,143,438

APPARATUS FOR COATING WEB MATERIAL Filed July 26, 1960 2 Sheets-Sheet 2 FIG.7

INVENTOR.

MARK CAMPBELL United States Patent Ofiice 3,143,438 Patented Aug. 4, 1964 3,143,438 APPARATUS FOR COATING WEB MATERIAL Mark Campbell, Keyser, W. Va., assignor to West Vii'" ginia Pulp and Paper Company, New York, N.Y., a corporation of Delaware Filed July 26, 1960, Ser. No. 45,445 18 Claims. (Cl. 118-104) This invention relates to improvements in apparatus for coating web material as, for example, paper and paperboard for high grade printing operations. The invention relates generally to blade coating and is useful in applying coatings to traveling webs on a paper-machine. It may also be used, however, in off-machine coating operations to coat moving webs.

Methods employed in most coating operations on paper and paperboard may be classed generally as roll coating or blade coating. Both methods, while being used extensively, possess some inherent characteristics which in certain instances make their use undesirable. In the former method, a layer of coating material is deposited upon a traveling web of paper by being transferred from a coating applicator roll in contact with the web. It is difiicult to produce a smoothly coated web in this manner because of the formation of a pattern upon the coated surface. This pattern is often referred to as a nip or roll pattern and in the manufacture of high grade papers, it may be objectionable.

It has long been known in the art that coating may also be applied to paper through the smoothing and wiping action of a doctor blade. In such coaters, the blade may serve as part of the boundary for the coating pond, through which the web to be coated is passed. In other coaters, the coating is applied to a traveling web by an applicator roll, and the blade serves to meter and smooth the coating which is thus applied.

Blade coaters are used extensively in the manufacture of high grade printing papers because of their ability to apply smooth coatings. However, problems of streaking of the coating often arise due to contaminant particles collecting under the blade. Such particles have dificulty in passing under the blade and tend to streak the coating on the moving web.

The present invention falls into the latter category of blade coaters, and belongs to the specific type of blade coaters modified by use of a doctor rod as the metering and smoothing device acting on the coating during application.

Streaking of the coating is greatly reduced when the metering and smoothing device is a cylindrical doctor rod since the rod will tend to pass contaminant particles such as grit, fibers, or dry lumps of coating material. Streaking may be reduced even more by rotating the rod, and the passing of contaminant particles by a rotating rod pneumatically loaded is greatly enhanced due to the pressure characteristics of the pneumatic device. However, some inconveniences are encountered in connection with the use of rod coating devices, and this invention provides for overcoming these diificulties.

The doctor rod is usually held by a flexible bearing member, known as a socket, which partially surrounds the rod. During certain coating operations, the rod is rotated in the direction of Web travel. Coating remains on the rod due to the film splitting action of the coating between the traveling web and the rotating rod. The coating on the rod tends to build up at the ingoing edge of the socket because the excess coating on the rod is only partially doctored off by the socket bearing. After a period of running, this build-up contacts the web and is transferred to the web in the form of coating droplets, impairing the smoothness of the already smoothed web.

With the rod rotating counter to the direction of web travel, in certain instances it has been found that excess coating material on the rod will be carried by the rod into the channel between the rod and socket bearing member. As the coating operation continues, the amount of coating in this channel builds up to the point that some coating is carried through the channel by the rotating rod to the outgoing rod-paper nip and is redeposited as coating droplets on the already smoothly coated Web.

The present invention provides for new and useful pneumatically loaded doctor rod coating devices. The invention also provides a doctor rod coating device whereby excess coating is removed from the rotating doctor rod, and coating carry through by the rod is prevented.

It has been found that coating carry through by the doctor rod in a coating device can be eliminated through the action of a flexible doctor blade bearing against the rod. As the rod rotates counter to the direction of web travel and meters and smooths the coating onto the web, the doctor blade acts on the rod to remove excess coating from the rod and prevents coating from being carried around the rod and redeposited on the smooth, coated Web. The doctor assembly consists of a small diameter cylindrical rod mounted between a thin metal rod holder or rod receiving member and a flexible doctor blade. The blade exerts a supporting force on the rod, and maintains the position of the rod with relation to the rod holder. Pressure for coat weight control may be supplied by pneumatic loading or flexing of a secondary blade, the preferred method being pneumatic loading. A dilatable fluid pressure device extends the full length of the rod holder and is disposed to urge the rod holder and the rod contained therein evenly along a predetermined, defined path toward the Web material, and means is provided for supporting the Web against the rod pressure with a counter pressure which is exerted substantially directly along said path.

The invention will now be more fully described with reference to the accompanying drawing forming part of this specification in which:

FIGURE 1 is a diagrammatic view, in side sectional elevation, of typical coating apparatus employing the novel doctor rod device in accordance with the present invention.

FIGURE 2 is a partial detailed plan view of the novel doctor rod holder forming part of the invention.

FIGURE 3 is a cross-section view of FIGURE 2.

FIGURE 4 is an enlarged cross section view of the coating apparatus of FIGURE 1.

FIGURE 5 is a cross-section view of another embodiment of the novel doctor rod assembly.

FIGURE 6 is a further embodiment of the novel doctor rod holder apparatus.

FIGURE 7 is a fragmentary view illustrating means for rotating the doctor rod.

An illustrative coating device employing the features of the present invention is incorporated in the coater of FIGURES 1 to 4. A paper web P is supported by backing roll 10 and passes between the nip formed by roll 19 and a coating applicator roll 11 from which coating is transferred to web P as roll 11 rotates in the direction of Web travel and carries coating 12 from the coating pan 13 into the nip formed by the backing roll 10, web P, and applicator roll 11. The backing roll 19 is driven at a circumferential speed equal to the linear speed of the traveling web P.

Excess coating is doctored from web P by doctor rod 14, falls onto applicator roll 11, and is carried back into the coating pan 13. To facilitate in removing excess coating from the doctor rod 14 and thus prevent coating carry through, a flexible doctor blade 15 bears against the flexible, cylindrical rod 14 and removes the excess coating which tends to adhere to rod 14. Doctor rod 14 is preferably driven counter to the direction of web travel to smooth and meter coating applied to web P.

The unique doctor rod assembly is best illustrated'in FIGURES 2 and 3. Doctor rod 14 is'mounted between a flexible doctor blade 15 and a thin metal rod holder 16, the latter being rounded or curved at the top to conform with the shape of rod 14 and to surround the rod in the order of about 90 degrees of the circumference of the rod. Doctor blade 15, the top end of which bears approximately tangentially against the rod 14 at a point approximately diametrically opposite the center of the curved top of the rod holder 16, exerts a supporting force on rod 14 and maintains the position of rod 14 with relation to the rod holder 16 by forcing the rod 14 into or against the curved top of rod holder 16. Rod holder 16 is mounted near its lower end on blade 15 and held in this position by rivets 17 across the width of the rod holder 16 and flexible doctor blade 15. Retaining buttons 18 are mounted on the lower end of blade 15 for the purpose of holding the doctor rod assembly in the pneumatic tube holder 19.

The novel doctor rod assembly is mounted in the pneumatic tube holder 19 as illustrated in FIGURE 4. Retaining buttons 18 on the end of blade 15 are held in a grooved portion 20 between retaining plate 21 and the pneumatic tube holder 19. The retaining plate 21 is held to the pneumatic tube holder 19 across its width by threaded screws 22 having their threaded bodies passed inward through retaining plate 21 and threaded into the pneumatic tube holder 19. The cutout portion 20 thus formed between the retaining plate 21 and the pneumatic tube holder 19 is slightly larger in cross sectional area than the retaining buttons 18, allowing for some freedom of slippage to facilitate blade removal.

The doctor rod assembly is pressed toward the backing roll 10 along which the rod 14 bears by means of a dilatable fluid pressure device in the form of a pneumatic rubber tube 23. The tube 23 is 1 /2 inches OD. and is lodged within al /2 inch I.D. slotted stainless steel tube holder 24 forming a part of the pneumatic tube holder 19. One side of the stainless steel tube holder 24 is machined away to produce a opening through which the penumatic tube 23 contacts the angle rod holder 16 of the doctor rod assembly. The tube 23 extends the full width of the rod holder 16 and is confined within the tube holder 24 by means of end plugs (not shown) threaded into the holder 24; Pneumatic tubes other than rubber may also be employed, and the use of plastic tubes such as those made of vinyl resins (for example, Tygon) have been found to be satisfactory.

V The pneumatic tube holder 19 is rigidly mounted on the structural support 25 by means of threaded screws 26 having their threaded bodies passed inward through one side of the structural support 25 and threaded into the pneumatic tube holder 19.

It has been stated that doctor rod 14 rotates in its holder, preferably in a direction counter to the travel of web P. This may be accomplished by any known means such as is illustrated in FIGURE 7. Rotative force is applied to each end of rod 14 by drive shafts 30 driven by spur gears 31 from a larger cross machine drive shaft 32. The cross machine drive shaft 32 is driven by reversible motor 33 through the main drive shaft 34 with suitable universal joints 35 at each of the main drive shaft 34. The spur gears 31 and the ends of shafts 30 and 32 are supported in suitable bearing assemblies 36. The rod may be driven in either direction depending upon the direction of rotation of motor 33.

The preferred doctor rod employed is a inch diameter rod drawn to close straightness tolerance, polished, and plated with 0.002 inch of chromium. It has been found that a certain rod rotation is necessary to eliminate any coating buildup at the outgoing rod-paper nip as a result of film split, even with the rod rotating reverse to web travel. High solids coating .colors (606l% solids) have been employed satisfactorily with freedom of both carry through by the rod and coating buildup at the outgoing rod-paper nip by maintaining a minimum rod rotation counter to the direction of web travel of approximately l0 rotations per minute per 100 feet of web speed. Coating colors with solids contents as low as 53% have also been employed, and, in general, the coat weights applied have ranged from 4 to 13 pounds per ream (500 sheets, 25 x 38 inches) when using pneumatic tube pressures of from 15 to 50 pounds per square inch. i

The rod holder 16 is preferably made of stainless steel with a wall thickness of 0.028 inch. The holder 16 is preferably mounted by rivets across its Width to the flexible stainless steel doctor blade of dimensions 3 inches x .012 inch at a position about one inch from the bottom end of the doctor blade 15. As shown in FIGURE 3, the rod holder 16 preferably receives or wraps the rod in the order of about of the circumference of the rod.

An alternative embodiment of the doctor rod assembly is illustrated in FIGURE 5. Doctor rod 46 is mounted between a flexible doctor blade 41 and a rod holder or rod receiving member 42 in much the same manner as was previously described for the device in FIGURES 2 and 3. The device shown in FIGURE 5 has the further feature of having a removable doctor blade 41 for aiding in the changing of blade 41 or rod 46 whenever such replacement is necessary due to wear. The rod holder 42 has a U- shaped bottom portion or channel into which a doctor blade 41 may be slidably placed and removed when required. The doctor rod holder 42 is mounted on a flexible mounting blade 43 by means of rivets 44 spaced at regular intervals across its width. Retaining buttons 45 are located on the bottom of the mounting blade 43 and serve to hold the doctor rod assembly in the pneumatic tube holder 19 (FIGURE 4) as previously described.

A further alternative embodiment of the doctor rod assembly is illustrated in FIGURE 6 in which a thin nylon or polytetrafiuoroethylene (Teflon) bearing 50 A x l inch) has been cemented to the inside of the rod holder or rod receiving member 51 across its width to facilitate in reducing friction and prolonging the life of rod 52 as it rotates against the bearing 50. The doctor rod 52 is mounted between a flexible doctor blade 53 and the rod holder 51.- The rod holder 51 is fixedly attached to the doctor blade 53 intermediate of blade 53 and near the bottom of rod holder 51 by rivets 54 spaced at regular intervals across its width. Retaining buttons 55 are provided at the bottom of blade 53 for insertion into the pneumatic tube holder 19 (FIG. 4) as previously described.

In each of the illustrative forms of the present invention the primary function of the doctor rod has been to spread, meter, and smooth the coating composition previously applied to the traveling web. However, arrangements in which the doctor rod assembly forms a part of the apparatus for applying the coating are also to be regarded as comprehended Within'the scope of the invention.

While certain preferred embodiments of the invention have been illustrated and described in detail, it is to be understood that changes may be made therein and the invention embodied in other structures. Hence, the present embodiments are therefore to be considered as illustrative and not as restrictive, and to cover the invention in whatever form its principles may be utilized.

I claim:

l. A coating device for web material comprising, in combination, a backing roll on which a Web may be caused to travel, a coating applicator roll opposed thereto for applying coating material to the web, a flexible metering and smoothing cylindrical doctor rod opposed to the backing roll and engageable with the web having undried coating material thereon, means for rotatively driving the rod, a rod receiving member rotatively supporting and partially surrounding the rod, a flexible rod cleaning doctor blade attached at an intermediate position thereof to the rod receiving member to mount said rod receiving member, one end of said doctor blade bearing against the doctor rod to flexibly hold the rod against the rod receiving member and to remove excess coating from the rod as the rod rotates to meter and smooth the coating on the web, a rigid support on which the other end of said doctor blade is mounted and a fluid pressure device extending substantially the full length of the rod receiving member to urge the rod receiving member and doctor rod toward the backing roll.

2. A device as set forth in claim 1 in which the doctor rod is driven counter to the direction of web travel.

3. A device as set forth in claim 2 in which the doctor rod is driven counter to the direction of web travel at a rate of at least revolutions per minute per 100 feet of web travel to eliminate coating buildup at the outgoing rod-paper nip when the solids content of the coating employed to coat the Web is at least 53 4. A device as set forth in claim 1 in which the rod receiving member wraps the doctor rod in the order of about 90 degrees of the circumference of the rod.

5. A device to meter and smooth coating material applied to a traveling web comprising, in combination, a flexible cylindrical doctor rod, a rod receiving member rotatively supporting and partially surrounding the rod and having a blade receiving channel at one end thereof, a flexible doctor blade slidably mounted at one end in the blade receiving channel of the rod receiving member and having its opposite end bearing against the doctor rod to flexibly hold the rod against the rod receiving member and to remove excess coating from the rod as said rod meters and smooths coating material on the web, and a flexible mounting blade attached to the rod receiving member to mount said rod receiving member.

6. A device to meter and smooth coating material applied to a traveling web comprising, in combination, a flexible cylindrical doctor rod, means connecting with the rod for rotatively driving the rod, a rod receiving member rotatively supporting and partially surrounding the rod and having a U-shaped end portion, a flexible doctor blade slidably mounted at one end in the U- shaped end portion of the rod receiving member and having its opposite end bearing against the doctor rod to flexibly hold the rod against the rod receiving member and to remove excess coating from the rod as said rod rotates to meter and smooth coating material on the web, said doctor blade being easily removable by slidably removing said blade from the blade receiving end portion of the rod receiving member, and a flexible mounting blade attached to the rod receiving member to mount said rod receiving member.

7. A device to meter and smooth coating material applied to a traveling web as set forth in claim 6 in which the rod receiving member is faced with a flexible, antifriction, plastic bearing material opposed to the doctor rod for intimate engagement with said doctor rod.

8. A device to meter and smooth coating material applied to a traveling web as set forth in claim 7 in which the plastic bearing material is a material selected from the group consisting of nylon and poly-tetrafluoroethylene.

9. A coating device for web material comprising, in combination, a web backing roll on which a web may be caused to travel, a coating applicator roll opopsed thereto for applying coating material to the web, a flexible cylindrical doctor rod opposed to the backing roll and engageable with the web having undried coating material thereon, means connecting with the rod for rotatively driving the rod, a rod receiving member rotatively supporting and partially surrounding the rod and having a blade receiving channel at one end thereof, a flexible doctor blade slidably mounted at one end in the blade receiving channel of the rod receiving member and having its opposite end bearing against the doctor rod to flexibly hold the rod against the rod receiving member and to remove excess coating from the rod as said rod rotates to meter and smooth the coating on the web, a flexible mounted blade attached to the rod receiving member to mount said rod receiving member, a rigid support on which the flexible mounting blade is mounted, and a fluid pressure device extending substantially the full length of the rod receiving member to urge the rod receiving member and the rod toward the backing roll.

10. A coating device as set forth in claim 9 in which the doctor rod is driven counter to the direction of web travel.

11. A device to meter and smooth coating material applied to a traveling web comprising, in combination, a flexible cylindrical doctor rod, a rod receiving member one end of which is curved to rotatively support and surround the rod in the order of about degrees of the circumference of the rod, and a flexible doctor blade for mounting said rod and rod receiving member and for cleaning said rod, said blade attached at an intermediate position thereof to said rod receiving member, one end of which blade bears approximately tangentially against the rod at a point approximately diametrically opposite a center portion of the curved end of said rod receiving member to flexibly hold the rod against the rod receiving member and to remove excess coating from the rod as the rod meters and smooths coating material on the Web, the other end of said blade extending beyond the rod receiving member for mounting said rod and rod receiving member on a rigid support.

12. A device to meter and smooth coating material applied to a traveling web comprising, in combination, a flexible cylindrical doctor rod, a rod receiving member one end of which is curved to rotatively support and surround the rod in the order of about 90 degrees of the circumference of the rod, and a flexible doctor blade for mounting said rod and rod receiving member and for cleaning said rod, said blade attached at an intermediate position thereof to said rod receiving member, one end of which blade bears approximately tangentially against the rod at a point approximately diametrically opposite a center portion of the curved end of said rod receiving member to flexibly hold the rod against the rod receiving member and to remove excess coating material from the rod as the rod meters and smooths coating material on the web, the other end of said blade extending beyond the rod receiving member and having means mounted thereon at the terminal portion of said blade for retaining said blade in a rigid support.

13. A device to meter and smooth coating material applied to a traveling Web comprising, in combination, a flexible cylindrical doctor rod, a rod receiving member one end of which is curved to rotatively support and surround the rod in the order of about 90 degrees of the circumference of the rod, a flexible doctor blade for mounting said rod and rod receiving member and for cleaning said rod, said blade attached at an intermediate position thereof to said rod receiving member, one end of which blade bears approximately tangentially against the rod at a point approximately diametrically opposite a center portion of the curved end of said rod receiving member to flexibly hold the rod against the rod receiving member and to remove excess coating from the rod as said rod meters and smooths coating material on the web, and a rigid support on Which the other end of said blade is mounted, said blade providing the sole rod cleaning element and the sole connecting element between said rigid support and said rod and rod receiving member.

14. A device to meter and smooth coating material applied to a traveling web comprising, in combination, a flexible cylindrical doctor rod, means connecting with said rod for rotatively driving said rod, a rod receiving member one end of which is curved to rotatively support and surround the rodin the order of about 90 degrees of the circumference of the rod, a flexible doctor blade for .mounting said rod and rod receiving member and for cleaning 'said rod, said blade attached at an intermediate position thereofto said rod receiving member, one end of which blade bears approximately tangentially against the rod at apoint approximately diametrically opposite a center portion of the curved end of said rod receiving member to flexibly hold the rod against the rod receiving member and to remove excess coating from the rod as the rod rotates to meter and smooth coating material on the web, and a rigid support on which the other end of said blade is mounted, said blade providing the sole rod cleaning element and the sole connecting element between said rigid support and said rod and rod receiving member.

15. A device as set forth in claim 13 in which the rod receiving member is faced with an anti-friction, plastic bearing material opposed to the doctor rod for intimate engagement with said doctor rod.

, 16. A device as set forth in claim 15 in which the antifriction bearing material is selected from the group consisting of nylon and polytetrafluoroethylene.

17. A device to meter and smooth coating material applied to. a traveling web comprising, in combination, a flexible cylindrical doctor rod, a rod receiving member one end of which is curved to rotatively support and surround the rod in the order of about 90 degrees of the circumference of the rod, a flexible doctor blade for cleaning said rod, said blade attached to said rod receiving member, one end of which blade bears approximately tangentially against the rod at a point approximately diametrically opposte a center portion of the curved end of said rod receiving member, and a rigid support on which the other end of said blade is mounted.

18. A device as set forth in claim 17 in which means connect with said rod for rotatively driving said rod. 4

References Cited in the file of this patent UNITED STATES PATENTS 1,566,358 White Dec. 22, 1925 2,695,004 Montgomery et a1 Nov. 23, 1954 2,729,192 Warner J an. 3, 1956 2,874,674 Hornbostel Feb. 24, 1959 2,946,307 Warner July 26, 1960 3,001,390 Zimmer Sept. 26, 1961 3,029,779 Hornbostel Apr. 17, 1962 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,143,438 August 4, 1964 Mark Campbell It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected belo Column 3, line 66, after "each"' insert end columr 5, line 68, for opopsed" read opposed column 6, line 6, for "mounted" read mounting column 8, line 9, for "'opposte" read opposite Signed and sealed this 24th day of November 1964.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER A-ttesting Officer Commissioner of Patents 

17. A DEVICE TO METER AND SMOOTH COATING MATERIAL APPLIED TO A TRAVELING WEB COMPRISING, IN COMBINATION,A FLEXIBLE CYLINDRICAL DOCTOR ROD, A ROD RECEIVING MEMBER ONE END OF WHICH IS CIRVED TO ROTATIVELY SUPPORT AND SURROUND THE ROD IN THE ORDER OF ABOUT 90 DEGREES OF THE CIRCUMFERENCE OF THE ROD, A FLEXIBLE DOCTOR BLADE FOR CLEANING SAID ROD, SAID BLADE ATTACHED TO SAID ROD RECEIVING MEMBER, ONE END OF WHICH BLADE BEARS APPROCIMATELY TANGENTIALLY AGAINST THE ROD AT A POINT APPROXIMIATELY DIAMETRICALLY OPPOSTE A CENTER PORTION OF THE CURVED END OF SAID ROD RECEIVING MEMBER, AND A RIGID SUPPORT ON WHICH THE OTHER END OF SAID BLADE IS MOUNTED. 